FR: Add dimension labels in guide_legend_cross() #79
Description
Hi,
Here is an idea on specific, yet common cases: crossed comparisons.
For instance, one could imagine a plot for a diagnosis test, with matching cases being plain while non-matching cases being dimmed.
The plot would have 2 colors (positive/negative) and 2 alphas (matching/ non-matching).
However, the default alpha legend is not very intuitive, and it would be much better IMHO if it could be "crossed".
An example is worth a thousand words, so here is a clumsy one using patchwork:
library(tidyverse)
library(patchwork)
set.seed(0)
df = expand.grid(x=1:5, tag1 = c("+", "-"), tag2=c("+", "-")) %>%
mutate(y = runif(n()))
p = df %>%
ggplot() +
aes(x = x, y = y, fill=tag1, group=tag1, alpha=tag1==tag2) +
geom_col(position = 'dodge', show.legend=FALSE) +
scale_alpha_manual(values=c(0.5, 1))
legend = df %>%
distinct(tag1, tag2) %>%
ggplot() +
aes(x = fct_rev(tag1), y = tag2, fill=fct_rev(tag1), group=tag1, alpha=tag1==tag2) +
geom_tile(width=0.9, height=0.9, show.legend=FALSE) +
scale_alpha_manual(values=c(0.5, 1)) +
scale_x_discrete(position = "top") +
coord_equal() +
labs(x="Disease", y="Test") +
theme_minimal()
wrap_plots(p, legend, widths=c(6,1))Created on 2025-05-30 with reprex v2.1.1
I have no idea how to implement that from inside ggplot2, but I'd be amazed by a legendry feature that would allow something like:
p +
guides(
fill = guide_2d_custom(by=alpha)
) Would this be a reasonable feature request?